Resolution

[AndrewEllinas]

What resolution should I use in Photoshop for my photos.

I'm using a 10D with the largest file size and quality (not RAW). When I bring the image into Photoshop, what resolution should I specify for the file so that I will be able to make really good quality prints?

[Roger_Cavanagh]

Andrew,

It will depend on your printer, but I would suggest 300 DPI as a good starting. That's a good number for Epsons, but I believe different makes may work best at other numbers.

You might be able to go as low as 240, but the best thing is to make a few tests to see what the reuslts look like.

Regards,

[md34]

I also have a similar question. In PS 7, under "image, image size", does it make a difference to just bump the DPI from the default 180 that the Canon 10D saves at, to 300 as most people seem to prefer? Also if I uncheck "resample Image" does this just increase the DPI and provide some benefit? Because otherwise, the picture just gets even bigger by changing the DPI to 300. What's the difference between doing this and just printing from photoshop and scaling the picture at the print preview screen?

Thanks to anyone with advice, sorry for the long post.

-mike

[john_houghton]

When you resize an image without resampling, altering the PPI (pixels per inch) will result in a change in the linear dimensions of the image. Thus, if your image is 5" wide at 300PPI ( total of 5 x 300 = 1500 pixels) and you change the PPI to 600, the width of the image will become 2.5". The width in pixels remains the same at 1500 (2.5 x 600).

When you resize an image and resample, the number of pixels is no longer fixed. You can change any two parameters from PPI, pixel dimensions, and linear size, and the third parameter will be automatically determined in line with the relationship linear size = pixel size divided by PPI.

When you increase the number of pixels by resampling, an interpolation process will create suitable RGB values for the new set of pixels, but this cannot increase the amount of detail in the image. However, the better interpolation functions may reduce the incidence of "jaggies" on diagonal edges and give a superior looking image.

When you decrease the number of pixels by resampling, you loses detail in the image, which cannot subsequently be recovered. So if you resample an image from 1000 x 1000 to 4 x 4 and then resample the 4 x 4 image back to 1000 x 1000, you will not restore the image to its former glory (try it!).

By default, Photoshop will print an image at the linear size reported in the Image Size dialog, i.e. pixel dimensions divided by PPI. You can allow Photoshop to resize the image in Print with Preview by using the scaling options and this will be satisfactory for most purposes, but you must expect a loss of quality when stretching small images over a large print area. Or you can resize it yourself and exercise more control. For best quality, you should resize without resampling to maintain a minimum of 200PPI (some would say 300PPI, others will say 240PPI - take your pick).

John

[AndrewEllinas]

Thanks for your answer John. Its kind of you to take the time an effort to make such a detailed post.

Naturally it raises further questions.

1) I've found that when I open an image from my 10D using Photoshop that the dpi defaults to 72. So I've been copying the image, opening a new blank image in photoshop at 300 dpi and pasting my photo in. This doesn't seem like it can be right - is there a better way to do this?

2) What is the best way to size an image for printing to maximise its quality? It seems to me that I can make an image smaller thus increasing its dpi but resampling to increase size will result in a loss of quality. So I guess its the same as with film, if I selectively enlarge one section of an image I can expect a loss in quality to result.

Regards

Andrew Ellinas

[john_houghton]

AndrewEllinas wrote:
1) I've found that when I open an image from my 10D using Photoshop that the dpi defaults to 72. So I've been copying the image, opening a new blank image in photoshop at 300 dpi and pasting my photo in. This doesn't seem like it can be right - is there a better way to do this?
If you want to change the resolution setting of the image to 300ppi, all you need do is open your 10D image and then do Image->Image Size and change the resolution to 300 (with resample unchecked). The linear dimensions will of course change in proportion, in line with my earlier explanation. But what exactly are you trying to achieve? If you want a print at 7" x 5", then resize without resampling to 7" x 5". (You will need to crop to get this aspect ratio, of course). The ppi will then be around 400, which is fine.

2) What is the best way to size an image for printing to maximise its quality? It seems to me that I can make an image smaller thus increasing its dpi but resampling to increase size will result in a loss of quality. So I guess its the same as with film, if I selectively enlarge one section of an image I can expect a loss in quality to result.
What you say is correct, but you should maybe take into account that large prints are generally viewed from a larger distance. If there aren't enough pixels to give you at least 200ppi in the print, it will be a good idea to upsample the image to 300ppi, say. After sharpening, this can give you the appearance of a nice sharp image, though detail will be lacking. This will show in areas like foliage and grass, which may be smudgy instead of showing individual leaves and blades.

There are various techniques advanced for upsampling to give best quality (e.g. upsample in several small steps rather than one big step), and there's the well known Genuine Fractals plugin, which is said to be worthwile for really large poster size prints.

Don't overlook the crop tool for resizing and cropping in one operation. E.g. Just specify 7" x 5" together with 300ppi in the options boxes and drag out the required crop area.

John

[AndrewEllinas]

Thanks John, you've been really helpful and I'm grateful.

I've just done a test photo, resized and cropped at 409.6 dpi and printed at 7x5. So I think I finally understand the principal.

A resize to 11x7 gives me a dpi of 280 and 16x11 gives me a dpi of 185. To produce a good quality print, what is the minimum dpi i should work with?

[john_houghton]

AndrewEllinas wrote:
A resize to 11x7 gives me a dpi of 280 and 16x11 gives me a dpi of 185. To produce a good quality print, what is the minimum dpi i should work with?
There's no magic figure. Big prints are usually viewed from further away so a lower resolution can provide acceptable quality, and a lot depends on the content of the image. If you insist on viewing all prints, regardless of size, at close quarters with a loupe, you will want 300 or more pixels per inch and you will want as many dots per inch as you can muster on the printer. (I think it's useful to distinguish between pixels and dots).

John

[The Photo Tuell]

AndrewEllinas wrote:1) I've found that when I open an image from my 10D using Photoshop that the dpi defaults to 72. So I've been copying the image, opening a new blank image in photoshop at 300 dpi and pasting my photo in. This doesn't seem like it can be right - is there a better way to do this?


Man, what some people will go through to get 300 DPI. It's not necessary, you are wasting your time.

Try doing some test prints instead of just looking at the numbers and believing what you've been told is best. If I had believed that I needed 300 DPI for everything I'd never have done this award winning 20x30 print from a G2.

DPI is so overrated, it's not funny anymore. Sure more DPI may be better, but you can get great results from lower DPI too. Larger prints are usually viewed from farther away so the DPI doesn't matter as much.

When getting pictures ready to print I don't worry about the DPI, I just crop to the right ratio (of pixels).

Hope this helps you not waste so much time with DPI. :)

[msvadi]

The Photo Tuell,
what you saying makes sense. I printed 11x14 images (something like 150 ppi) with G2 that looked very well. I could not detect pixelation.

My question is if anyone tried to compare large prints with resampling to 300 ppi and without. How big is the difference? I understand that interpolation cannot create something that is not in the picture already, no matter how sophisticated the interpolation algorithm. I'm just curious if there is any difference, and if the resampled image does not, actually, turn worse.

[CyberDyneSystems]

The DPI resolution settings in PS have no effect on the actual resoltion of the image shot.. you still have the specific pixels. (ps 72 dpi is your PC screens resolution in DPI, thats why it tends to be the default,. as that is what you are viewing of the iamge is veiwed at 100%)

I and many others ignore the "300DPI and 8"X10" " settings in photoshop. Simply print to scale of the paper used and you will get the best scale that your original file can produce at that specific print size without upscaling resolution.

The only time I would be concerned is when I am printing at print sizes far beyond the cameras image file size. In which case it may be better to upscale or interpolate the image using a utility or photoshop at the file end of things as opposed to on the printer side...

??? does any of this make any sense?

[CyberDyneSystems]

msvadi wrote:


My question is if anyone tried to compare large prints with resampling to 300 ppi and without. How big is the difference? I understand that interpolation cannot create something that is not in the picture already, no matter how sophisticated the interpolation algorithm. I'm just curious if there is any difference, and if the resampled image does not, actually, turn worse.


My understanding is that a tool like "Genuine Fractals" can do a fairly significantly better job at interpolation that say Photoshops printer scaling. But again I would argue that if you start with a 6 megapixel image it will be a very large print indeed that would neccesitate the added help availble in such a software tool.

I also understand that a lot of the reason for the deining of DPI and image size setting within Photoshop was merely to fascilitate outside print jobs,. if the file is sent to the outside printshop with the print size and dpi built in there can be fewer chances for error.

Im my humble opinion,. for those of us who print at home with our own printers, we have little need of these settings. Again they don't actaully change the file unless you implent interpolation.. they are instaed a mao as to how the existing files pixles should be laid on paper.